Oilfield wells include the use of sucker rods consisting of 25 to 30 foot lengths of solid rods with male threads at each end, threaded together into a rod string that connect the downhole oil well pump to the surface reciprocating drive that in its entirety brings liquid hydrocarbons from deep within the ground to the surface.
Each sucker rod threaded male end is screwed into a rod coupling or collar or box so that the shoulder of each rod end is tightened against the shoulder of the rod coupling. The connected and tightened assembly of sucker rod connected to a rod coupling which is connected to the next sucker rod forms the rod string.
The tightening of each sucker rod threaded connection to a specific circumferential displacement from a hand tight shouldered circumferential position is the method determined by the sucker rod manufacturers to achieve the correct tightness between the sucker rod and the sucker rod collar. Inaccurate tightness of a connection can cause failure of the sucker rod string within the well bore.
Hundreds of sucker rod connections typically comprise a rod string in oil wells. Sucker rod connections are critical to the operational life of a sucker rod string.
Currently hydraulically powered sucker rod tongs are commonly used to assemble and disassemble a string of sucker rods. Current practices involve screwing the sucker rod connections together manually or with hydraulic powered sucker rod tongs to the shoulder of the connection and then without stopping the sucker rod tongs, they apply rotational torque between the upper and lower sucker rod connections using the hydraulically powered sucker rod tong and engage the upper and lower sucker rod segments on their respective mating rod flats to the rod coupling. The rod coupling provides the connection between sucker rods. Activating the hydraulically powered sucker rod tongs rotates one sucker rod thread relative to the other sucker rod thread to achieve a tight connection. As the connection tightens, the tong ultimately stalls at the hydraulic pressure preset by the operator assuming the achievement of a corresponding torque and circumferential displacement movement of the sucker rod connections relative to each other. When the tong rotationally stalls, the operator assumes that the connection has achieved the predetermined circumferential displacement position and is properly torqued.
The position at which the rod connections displace from the hand tightened shouldered circumferential position is not predictable. Frequently, the operator tests the position at which the force of the hydraulically powered sucker rod tongs tightens the connection to and the operator measures that distance in comparison to a known circumferential displacement scale or CD Card. The hydraulic pressure setting of the hydraulic circuit is adjusted to approach the displacement result desired. This is an inaccurate, unreliable and unpredictable method of achieving a circumferential displacement from a known position. Repeatability of hydraulic relief valves is dependent on oil flow, viscosity and fluid pressure drops. Variations within the relief valves ability to repeat this setting can exceed 10%. The hydraulic motor that delivers the torque to the hydraulically powered tong assembly within its design can vary its output torque given the same input hydraulic pressure throughout 1 revolution of the motor. The motor can have as few as 5 power strokes per revolution and output torque can exceed ±20% specifically due to the rotational position that the motor is in as torque is being applied to the sucker rod connections. The force which is required to rotate different sucker rods and couplings can vary significantly resulting in significant differences in final circumferential displacement. The result of the current sucker rod hydraulic powered tongs design is that circumferential displacement of the sucker rod connection from a hand tightened shoulder circumferential position is not predictable or reliable.
It is, therefore, desirable to provide a sucker rod tong that can tighten sucker rod connections to an accurate, repeatable and reliable circumferential displacement from a shoulder position.